1. Field of the Invention
The present invention is related to telecommunications, and in particular to echo management or cancellation in an Internet Protocol communications network.
2. Description of the Related Art
The use of Fax over Internet Protocol (FoIP) has become increasing popular. One reason for the increasing popularity of FoIP is the potential for significant reductions in facsimile related costs.
However, certain technical challenges are posed to systems using FoIP. For example, echoes can interfere with FoIP performance. There are several forms and causes of echo in the Public Switched Telephone Network (PSTN). For example, an echo can be caused by poor quality analog and digital telecommunication terminals (handsets, fax machines, etc.). An echo can be caused by background noise of the caller and called party. In addition, an echo can be caused by signal reflections generated by a circuit that converts between a 4-wire circuit, which includes two transmit wires and a 2-wire circuit, that includes one transmit wire and one receive wire.
In many instances, echo is not a very serious problem with a conventional PSTN-based fax communication, as roundtrip delays are typically less than 50 ms. However, echo becomes a serious problem when a packet switched system is used in the communications path, such as in Fax-over-Internet Protocol (FoIP) networks, because the round-trip delay through the network is often greater than 50 ms. This echo interferes with the Fax T.30 and T.4 protocols used by fax machines/servers to establish a call.